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.\" ========================================================================
.\"
.IX Title "UNIVERSAL::can 3"
.TH UNIVERSAL::can 3 "2020-07-07" "perl v5.32.0" "User Contributed Perl Documentation"
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.SH "NAME"
UNIVERSAL::can \- work around buggy code calling UNIVERSAL::can() as a function
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
To use this module, simply:
.PP
.Vb 1
\&  use UNIVERSAL::can;
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
The \s-1UNIVERSAL\s0 class provides a few default methods so that all objects can use
them.  Object orientation allows programmers to override these methods in
subclasses to provide more specific and appropriate behavior.
.PP
Some authors call methods in the \s-1UNIVERSAL\s0 class on potential invocants as
functions, bypassing any possible overriding.  This is wrong and you should not
do it.  Unfortunately, not everyone heeds this warning and their bad code can
break your good code.
.PP
This module replaces \f(CW\*(C`UNIVERSAL::can()\*(C'\fR with a method that checks to see if
the first argument is a valid invocant has its own \f(CW\*(C`can()\*(C'\fR method.  If so, it
gives a warning and calls the overridden method, working around buggy code.
Otherwise, everything works as you might expect.
.PP
Some people argue that you must call \f(CW\*(C`UNIVERSAL::can()\*(C'\fR as a function because
you don't know if your proposed invocant is a valid invocant.  That's silly.
Use \f(CW\*(C`blessed()\*(C'\fR from Scalar::Util if you want to check that the potential
invocant is an object or call the method anyway in an \f(CW\*(C`eval\*(C'\fR block and check
for failure (though check the exception \fIreturned\fR, as a poorly-written
\&\f(CW\*(C`can()\*(C'\fR method could break Liskov and throw an exception other than \*(L"You can't
call a method on this type of invocant\*(R").
.PP
Just don't break working code.
.SH "AUTHOR"
.IX Header "AUTHOR"
chromatic, \f(CW\*(C`<chromatic@wgz.org>\*(C'\fR
.SH "BUGS"
.IX Header "BUGS"
Please report any bugs or feature requests to \f(CW\*(C`bug\-universal\-can@rt.cpan.org\*(C'\fR,
or through the web interface at
<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=UNIVERSAL\-can>.  This will
contact me, hold onto patches so I don't drop them, and will notify you of
progress on your request as I make changes.
.SH "ACKNOWLEDGEMENTS"
.IX Header "ACKNOWLEDGEMENTS"
Inspired by UNIVERSAL::isa by Yuval Kogman, Autrijus Tang, and myself.
.PP
Adam Kennedy has tirelessly made me tired by reporting potential bugs and
suggesting ideas that found actual bugs.
.PP
Mark Clements helped to track down an invalid invocant bug.
.PP
Curtis \*(L"Ovid\*(R" Poe finally provided the inspiration I needed to clean up the
interface.
.PP
Peter du Marchie van Voorthuysen identified and fixed a problem with calling
\&\f(CW\*(C`SUPER::can\*(C'\fR.
.PP
Daniel LeWarne found and fixed a deep recursion error.
.PP
Norbert Buchmüller fixed an overloading bug in blessed invocants.
.PP
The Perl \s-1QA\s0 list had a huge... discussion... which inspired my realization that
this module needed to do what it does now.
.SH "COPYRIGHT & LICENSE"
.IX Header "COPYRIGHT & LICENSE"
Copyright (c) 2005 \- 2014, chromatic. This module is made available under the
same terms as Perl 5.12.